The present invention relates to a magnetic head used in a magnetic recording/reproducing apparatus such as a VTR or the like and a manufacturing method therefor.
Currently, Metal-In-Gap heads (hereinafter referred to as a "MIG head") are primarily used as magnetic heads in magnetic recording/reproducing apparatuses such as VTRs, etc. The MIG head has a magnetic alloy film of a high saturation magnetic flux density, e.g., Fe-Si-At, Fe-Ta-N or the like film provided in the vicinity of a ferrite head gap. The magnetic alloy film is formed on a ferrite core by a thin film forming method such as sputtering or a similar manner. Therefore, the MIG head is designed to improve recording characteristics, while making use of reproduction characteristics displayed in a conventional ferrite head.
A magnetic head in the simplest constitution is shown in FIG. 5A as an example of the aforementioned MIG head. In FIG. 5A, reference numerals 1-4 represent: 1 a ferrite core; 2 a magnetic alloy film; 3 a magnetic gap formed of SiO.sub.2 or the like; and 4 a core-bonding glass.
When Fe-Si-At, Fe-Ta-N or the like alloy is used for the magnetic alloy film 2 of the above-constituted magnetic head, an interfacial part between the ferrite core 1 and magnetic alloy film 2 is subject to counter diffusion, particularly, diffusion of oxygen in the ferrite core 1 into the magnetic alloy film 2 because of the thermal treatment in the manufacturing process, thus resulting in the generation of a nearly non-magnetic layer having a magnetic permeability greatly decreased.
FIG. 5B indicates a depth profile obtained by the Auger electron spectroscopy of an interface between the ferrite core and Fe-Ta-N alloy film in a diffused state after the heat treatment at 500.degree. C. for one hour. Only Fe, N and O signals are excerpted in the diagram. The diffusion of oxygen into the magnetic Fe-Ta-N alloy film is obvious in FIG. 5B. In other words, in the MIG head of the constitution with the interfacial part being parallel to the magnetic gap 3 (referred to as a "parallel MIG head"), an apparent gap (referred to as a "pseudo gap" below) different from the original magnetic gap 3 is disadvantageously formed at the interfacial part, which damages characteristics of the head. A level of a pseudo signal is approximately 5-10 dB although a practical level is 1 dB or lower.
In order to solve the above problem, such magnetic heads constituted as in FIGS. 6 and 7 are devised and put in practical use at present.
The magnetic head of FIG. 6 avoids the pseudo gap by inclining the interfacial part of the ferrite core 1 and magnetic alloy film 2 to the magnetic gap 3. That is, even if an apparent gap is generated at the inclined interfacial part, the gap is inclined to the original magnetic gap 3 and therefore not regarded as the above-discussed pseudo gap. In the constitution of FIG. 6, however, a head track width becomes hard to regulate due to the inclination of the magnetic alloy film 2, leading to high costs and a low yield.
Meanwhile, the interfacial part of the magnetic head between the ferrite core 1 and magnetic alloy film 2 is corrugated in FIG. 7, so that a potential pseudo gap at the interfacial part is definitely distinguished from the original magnetic gap 3. Although the problem of the pseudo gap is eliminated in this arrangement, an extra work which is difficult to carry out in the case of a narrow track is required to process the ferrite core 1 in corrugation.
A magnetic head constituted as in FIG. 8A is also put in practical use. The magnetic head in FIG. 8A is provided with a diffusion prevention film 6 of SiO.sub.2, Al.sub.2 O.sub.3, etc. which is formed and interposed by a thin film forming method such as sputtering or the like method at the interfacial part of the ferrite core 1 and magnetic alloy film 2 of the simple MIG head of FIG. 5A. Although the diffusion prevention film 6 particularly formed at the interfacial part of the ferrite core 1 and magnetic alloy film 2 in FIG. 8A is non-magnetic, the non-magnetic layer is formed in such a small thickness as up to approximately 10 nm thereby to prevent the counter diffusion, and the pseudo gap is restricted to a degree not obstructing the practical use of the magnetic head.
FIG. 8B is a depth profile according to the Auger electron spectroscopy obtained from an SiO.sub.2 diffusion prevention film formed about 7 nm thick at the interfacial part of the ferrite core and Fe-Ta-N film and thermally treated at 500.degree. C. for one hour. Fe, N, O and Si signals alone are excerpted in the profile. The diffusion is prevented more effectively than in FIG. 5B.
However, in the magnetic head provided with the diffusion prevention film as above, a minute change in film thickness, stress, adhering force or film structure of the diffusion prevention film 6 due to film formation conditions results in variations of the pseudo signal by 2 dB or so, thereby hindering the production of stable products.